Second-Order Active Low-Pass Filter (LM741)

Overview

This project implements a second-order active low-pass filter using the LM741 operational amplifier. The filter is designed in KiCad and is suitable for basic signal conditioning and noise filtering applications.

The filter attenuates frequencies above a specified cutoff frequency (fc) while allowing lower-frequency signals to pass with minimal attenuation.

Schematic

PCB Layout

Here’s a preview of the designed PCB:

The filter circuit is built using a Sallen-Key topology and includes:

• Op-Amp: LM741 (U1)
• Resistors: R1, R2, R3, R4
• Capacitors: C1, C2
• Input/Output: J1, J2 (Coaxial connectors), J3 (Pin connector)
• Power Supply: ±10V

(Replace component values and results below with your actual design)

Component	Value
R1	3.3 kΩ
R2	3.3 kΩ
R3, R4	10 kΩ
C1	10 nF
C2	10 nF
Cutoff	~4.8 kHz

Files Included

📁 KiCad Project Files

• Schematic: Second_Order_Low_Pass_Filter_Ac.kicad_sch
• PDF Schematic: Second_Order_Low_Pass_Filter_Ac.pdf
• PCB Layout: Second_Order_Low_Pass_Filter_Ac.kicad_pcb

📁 Fabrication Files

• Gerber Files: Ready for PCB manufacturing.
• Drill files and fabrication layers included.

📁 Bill of Materials (BOM)

• Can be generated from KiCad (Tools -> Generate BOM).

How to Use

1. View Schematic and PCB

   • Open .kicad_sch and .kicad_pcb files in KiCad (v9.0.2 or newer).

2. Simulate (Optional)

   • Export netlist and simulate in a tool like LTspice or use KiCad’s simulator for basic analysis.

3. Fabricate PCB

   • Use the included Gerber files to manufacture the PCB through a PCB fabrication service.

4. Assemble the Circuit

   • Solder components as per the schematic and BOM.
   • Power the board using ±10V.

5. Test the Filter

   • Apply test signals and verify the cutoff frequency response using an oscilloscope or signal analyzer.

Notes

• The LM741 is a general-purpose op-amp with limited bandwidth. For high-frequency applications, consider alternatives like TL072 or LM358.
• This filter is ideal for audio applications or low-frequency signal conditioning tasks.

License

GPL 3.0

Acknowledgments

Special thanks to the KiCad community for making open-source hardware design accessible!